Salman Abedi, whose terrorist attack on Monday night killed 22 people, is believed to have spent time in Libya during the 2011 uprising and was the child of an exiled Libyan couple who returned to fight.
It also emerged that Abedi had known links to Isis and had travelled to Syria before returning to the United Kingdom, according to France's interior minister.
A USA law enforcement official later authenticated the photos and said they had been provided by British authorities to American investigators, CNBC reported.
Pop star Ariana Grande said Friday that she will hold a benefit concert in Manchester, for the victims of Monday's suicide bombing at her show in the British city.
Abedi's movements just before the attack have also lent credence to the terror cell theory. Authorities in Tripoli have also said they are holding Salman's father, Ramadan Abedi, although the reasons for his detention were not disclosed.
Earlier this week the militia said Hashim had admitted - under interrogation - that he and Salman were members of ISIS.
Flowers and messages of condolence are left for the victims of the Manchester Arena attack.
Investigators are trying to find whether Abedi knew several Manchester-based jihadis, including Libyan man Abdalraouf Abdallah, who was jailed in the United Kingdom for terror offenses, and Raphael Hostey, an IS recruiter killed in Syria. Abedi's brother Hashem and father Ramadan were detained on Wednesday by one of the militia groups in Tripoli that claims to be an anti-terrorism force.
Authorities are investigating whether Abedi could have been stopped, after Libyan community members in Manchester reported concerns about his views.
British Home Secretary Amber Rudd said she had issued a plea to U.S. authorities not to leak.
Britain reduced its terrorism threat level a notch Saturday, from "critical" to "severe", yet security remained high as jittery residents tried to enjoy a long holiday weekend. His older brother, 23-year-old Ismail, was arrested by Manchester police on Tuesday.
"The British police have been very clear that they want to control the flow of information in order to protect operational integrity, the element of surprise, so it is irritating if it gets released from other sources, and I have been very clear with our friends that should not happen again", UK Interior Minister Amber Rudd said. Police raided homes believed to be connected with the investigation.
Prime Minister Theresa May has warned of another attack.
Donald Trump said that the relationship between the United States and Great Britain was the most cherished of all USA ties. He said the number of overall wounded was raised due to the "walking wounded" who came in hours after the attack.
"Many experts, including professionals in our intelligence and security services have pointed to the connections between wars we have been involved in or supported and and fought in other countries, such as Libya, and terrorism here at home", he said.